Has anyone found the secret to preserving the brilliant yellow color of freshly milled Bois d’Arc? (Osage Orange)

I have made a couple of pens and wine stoppers out of Bois d’Arc and I really like the eye catching bright yellow color. The problem is that the bright color doesn’t last and gives way to a rich brown shade over time. This isn’t entirley bad but I’d sure like to keep the vibrant color longer.